The present invention relates to a process intended for encapsulation of weakly polar organic products by interfacial polycondensation.
Interfacial polycondensation is a technique allowing in-situ manufacture of a polymer membrane at the surface of the droplets of an emulsion. This membrane is obtained by chemical reaction between two types of monomer so selected that the polymerization reaction takes place at the interface between the disperse phase and the continuous phase.
Encapsulation by interfacial polycondensation is a well-known technique (Microencapsulation: Methods and Industrial Applications, Edited by S. Benita, Marcel Dekker 1996) which generally involves two types of complementary monomers, one being soluble in the aqueous phase and the other in the organic phase. Examples of industrial applications of this technique are essentially known in the phytosanitary sphere (document FR-2,419,676 for example) for the production of insecticide, herbicide and fungicide microcapsules with polyamide, polyurea or polyurethane membranes, and in the biomedical and veterinary sphere.
The present invention relates in particular to the polycondensation of direct oil/water emulsions at the surface of droplets and to the formation of microcapsules whose core consists of a weakly polar organic product embedded in a polyamide membrane. The material to be encapsulated is either directly the weakly polar organic product, or another material or additive which is solubilized or dispersed in the weakly polar organic product.
The present invention thus relates to a process of obtaining microcapsules, comprising mainly the following stages:
preparing a scarcely water-soluble organic phase containing a determined amount of acid chlorides,
forming an emulsion of said organic phase in an aqueous phase,
adding to the aqueous emulsion an amount of at least one polyoxyalkylene polyamine,
reacting the monomers containing the amine and acid chloride functions so as to form a polyamide membrane around the emulsified organic phase,
recovering the microcapsules obtained.
The aqueous phase can contain a surface-active additive.
The additive can be a polymer having a surface-active function, for example partly hydrolysed polyvinylalcohol PVA.
The molar ratio R of the amine functions to the chloride functions can range between 1 and 30, preferably between 4 and 10.
The polyamine can be a diamine of general formula: 
with T methyl (CH3) or hydrogen (H), and n ranging between 2 and 40, preferably between 2 and 8.
In a variant, n is about 2.6.
In another variant, the polyamine can be a triamine of general formula: 
A is an alkyl group containing 1 to 20 carbon atoms, A preferably is an ethyl group,
T is methyl (CH3) or hydrogen (H),
x, y and z each range independently between 1 and 8.
The number of amine functions can furthermore be provided by adding diethylenetriamine.
Said acid chlorides can be selected from among sebacoyl chloride, trimesoyl chloride or mixtures thereof.
A mixture of sebacoyl and trimesoyl acid chloride can be respectively 90% and 10% in COCl functions.
The amount of acid chloride can range between 0.3 and 4 moles of COCl per milliliter of organic phase, preferably between 1 and 2 moles per milliliter.
The invention also relates to a microcapsule containing a scarcely water-soluble organic phase embedded in a polyamide membrane resulting from the reaction between at least one polyoxyalkylene polyamine and acid chlorides. According to the invention, the polyamine comprises at least one of the following amines:
a diamine of general formula: 
with T methyl (CH3) or hydrogen (H), and n ranging between 2 and 40, preferably between 2 and 8, and in particular n is about 2.6;
a triamine of general formula: 
A is an alkyl group containing 1 to 20 carbon atoms, preferably A is an ethyl group,
T is methyl (CH3) or hydrogen (H),
x, y and z each independently range between 1 and 8.
The acid chloride functions can be provided by sebacoyl chloride, trimesoyl chloride or mixtures thereof.
The amine functions can be provided by adding other polyamines, notably diethylenetriamine.
One of the main advantages of the process according to the invention is that it allows to control the thickness, the mechanical properties and the salting out properties of the polyamide microcapsule, on the one hand by controlling hydrolysis of the acid chloride by its initial concentration, the stirring time and the reaction time, and on the other by adding trifunctional monomers.
One of the applications of these capsules can be thermal insulation by using, as the organic phase, a rather insulating material, for example light-cut or other petroleum products, vegetable oils, glycol chemical derivatives, etc., convection being blocked by the encapsulated structure. Phase-change materials can be advantageously used, consisting for example of a mixture of chemical compounds from the alkanes family: paraffins, waxes, fatty alcohols, fatty acids, etc.
The acid chlorides (COCl) used can be selected, for example, from the following list:
adipoyl chloride
sebacoyl chloride
succinyl chloride
(meta, para) phthaloyl chloride
4,4-sulphonyldibenzoyl chloride
1,6-hexanedisulphonyl chloride
1,4-cyclohexanedicarbonyl chloride
1,2-ethanedisulphonyl chloride
4,4-biphenyldicarbonyl chloride
phosgene
dimethoxycarbonylterephthaloyl chloride
1,3,5-benzenetricarbonyl trichloride, or trimesoyl chloride.
Sebacoyl chloride and/or trimesoyl chloride, or mixtures thereof, are preferably used.
The polyoxyalkyleneamine used within the scope of the invention is a polyamine, preferably a di or triamine, sufficiently soluble in water, which can be defined by:
In the case of a diamine: 
where T can be methyl (CH3) or hydrogen (H), and n ranges between 2 and 40, preferably between 2 and 8.
Among these compounds, Jeffamine D-230 is the compound having for n a mean value of 2.6.
In the case of a triamine: 
with:
A an alkyl group containing 1 to 20 carbon atoms, A preferably is an ethyl group,
T is methyl (CH3) or hydrogen (H),
X, y and z each independently range between 1 and 8.
Among these compounds, Jeffamine T-403 (HUNTSMAN Int.): A ethyl, T methyl and x+y+z=5.3.
The other amines used in combination with the polyoxyalkylene polyamine can be:
ethylenediamine
hexamethylenediamine
piperazine
1,3-propylenediamine
tetramethylenediamine
p-phenylenediamine
bis(4-aminocyclohexyl)methane
1,4-bis(aminomethyl)cyclohexane
bis(p-aminophenyl)methane
1-lysine
4,4xe2x80x2-oxydianiline
4,4xe2x80x2-methylenedianiline
biopolymers, proteins, polysaccharides
diethylenetriamine
triethylenetetramine
tetraethylenepentamine.
The organic phase can be any weakly polar and scarcely water-soluble liquid (at working temperature). In an example according to the invention, the organic phase is a phase-change material, for example a paraffin or a mixture of paraffins. In this case, the working temperature must be higher than the melting temperature of the paraffin so as to be able to form a liquid/liquid emulsion for implementing the process.
The products used in the examples are (the identification names used afterwards are given in brackets):
Amines: Jeffamine D-230 (JA):
Code and name of the product 75 851 Jeffamine D-230
Supplier: HUNTSMAN Int. Trading Corp., Chemical name and/or family or description: Polyalkylamine, No. CAS: [9046-10-0], Aspect: transparent liquid.
Diethylenetriamine (DETA)
Supplier: ALDRICH, No. CAS [111-40-0], liquid.
Acid chlorides:
Sebacoyl chloride (CS)
Supplier: ALDRICH, No. CAS [111-19-3], liquid.
1,3,5-benzenetricarbonyl trichloride or trimesoyl chloride (TMC)
Supplier: ALDRICH, No. CAS [4422-95-1], solid.
Demineralized water
Paraffin LINPAR 18-20 marketed by CONDEA Augusta S.p.A.
Surfactant: Polyvinylalcohol (PVA)
Hydrolysed at 88%, Mw=22000 g/mol, supplier: JANSSEN CHIMICAxe2x80x94No. CAS [9002-89-5].
The protocol allowing the microcapsules to be obtained can be as follows:
a) Preparation of the Aqueous Solution of the Surfactant:
Dissolution at 60xc2x0 C. of the surfactant (PVA) at 1% by weight in 150 ml demineralized water.
b) Emulsification Stage:
In a double-walled reactor (circulating water at 28xc2x0 C.), the PVA solution is added to the 150 ml. Stirring is set at 600 rpm (6 PTFE blades), and 30 ml of the organic phase (paraffin Linpar 18-20) and the acid chloride(s) (CS or TMC or CS+TMC) are added dropwise. The emulsification time is 5, 15 or 60 minutes.
c) Polycondensation Reaction Stage Formation of the Capsules:
After the emulsion has formed, the stirring speed is set at 300 rpm. 150 ml of an aqueous solution of amines (JA or JA+DETA) is added dropwise (for about 10 minutes). The reaction progresses for 15 or 60 minutes according to the examples.
The total volume of emulsion is 330 ml, the PVA concentration is 0.5% in relation to water.
The respective amounts of amines and acid chloride are defined by a ratio R equal to the molar ratio of the amine functions to the acid chloride functions provided by the various constituents. R ranges between 1 and 30, preferably between 4 and 10, and in the following examples it is about 5, except in the presence of an inorganic base Na2CO3 where R is about 1. In the absence of an inorganic base, an amine function excess allows to neutralize at least partly the acidity formed during the polycondensation reaction.
When trifunctional compounds are used, the NH2 functions of JA and DETA are substantially distributed equitably.
When a mixture of TMC and CS is used, the proportion of the COCl functions is substantially 10% and 90% respectively.
In the following examples, 6, 20, 30, 60 or 100 millimoles of COCl are used in the 30 ml of paraffin type organic base.
d) Recovery of the Capsules:
At the end of the reaction, the capsules are recovered by discharging the aqueous phase. The separation is simplified by the density difference between the two phases, which allows creaming of the microcapsules to be observed. The capsules are washed three times with warm water, then three times with cyclohexane under vacuum filtration.
e) Drying of the Capsules:
Once recovered by filtration, the capsules are either freeze dried or dried at ambient temperature.
The encapsulation yield is estimated as follows: 30 ml cyclohexane is added to 50 ml of reaction mixture (aqueous solution+microcapsules). After magnetic stirring, the mixture is centrifuged for 10 minutes at 3000 rpm. The cyclohexane-paraffin mixture is recovered with a teat pipette, then the cyclohexane is evaporated under rotavap. The non-encapsulated paraffin recovered at the bottom of the drum is weighed. The yield is 100 times the ratio of the mass of paraffin recovered to the mass of initial paraffin.